An electrochemical gas sensor with a mediator dissolved in the electrolyte is known from DE 10 2004 062 051 A1. The presence of a mediator offers the possibility of providing sensors that are highly selective for the analyte gas. The mode of operation of a gas sensor with a mediator is based on the fact that analyte gas diffuses through the measuring electrode into the electrolyte solution and is oxidized or reduced by the mediator. The analyte is converted in the process into a decomposition product and the mediator into an intermediate product, which is reoxidized or re-reduced at the measuring electrode. The electron transfer needed for this, which is proportional to the percentage of analyte gas in the gas sample, can be detected as the measured current.
Electrochemical gas sensors with mediators are characterized by a low residual current, high long-term stability and low cross sensitivity to interfering gases. Suitable mediators are available so far for special detection reactions only. However, the sensitivity of detection of the electrochemical gas sensor is also affected by the electrode material of the gas sensor.
An electrochemical gas sensor with a plurality of electrodes and a measuring electrode made of diamond-like carbon (DLC) is known from DE 199 39 011 B1. The measuring electrode is produced by means of a coating process, in which diamond-like carbon is applied to a gas-permeable membrane by means of a sputtering process. The measuring electrodes made of DLC have very high long-term stability.
An electrochemical gas sensor with a measuring electrode consisting of boron- or nitrogen-doped diamond (BDD) is known from DE 101 44 862 A1. The measuring electrode material is applied as a thin layer to a porous, gas-permeable substrate. Such measuring electrodes have a very high long-term stability and an extremely large potential window, so that very difficult-to-oxidize substances can be reacted as well.
An electrochemical measuring device, in which the measuring electrode has carbon nanotubes, is known from DE 10 2006 014 713 B3. This sensor contains a mediator based on a transition metal, it selectively detects SO2 and avoids the formation of elemental sulfur, but has only a low sensitivity for H2S.